NORMAL VALUES FOR AMNIOTIC-FLUID INDEX DURING UNCOMPLICATED TWIN PREGNANCY

Objective: To establish the gestational age trends of amniotic fluid i ndex (AFI) in uncomplicated twin pregnancies. Methods: Amniotic fluid index was measured in uncomplicated twin pregnancies seen between 1985 and 1993 and meeting the following criteria: 1) no maternal medical o r obstetric complications, 2) normal growth of both twins by serial ul trasound, and 3) normal amniotic fluid volume by ultrasound. Amniotic fluid index was measured by adding the deepest vertical pockets in fou r quadrants, defined by the umbilicus and linea nigra. The relation be tween gestational age and AFI was evaluated using linear regression an alysis. Results: Two hundred eighty-two sets of twins were considered uncomplicated; 1101 AFI measurements were performed on these pregnanci es between 25.5 and 40.5 weeks' gestation. Percentile values for AFI w ere determined according to gestational age. The regression equation r elating the median to gestational age was: AFI = 19.4 - 0.12 x gestati onal age (P = .03). The R(2) value was 0.04. Conclusion: Gestational a ge trends in normative AFI measurements for twin pregnancies have been established. Their use will facilitate a more reproducible, quantitat ive diagnosis of oligohydramnios in twins, compared with subjective, q ualitative approaches to amniotic fluid volume assessment.